Want your ab training to work even better? Then "turn off" your hip flexors. If you limit hip flexor recruitment, your abs will have to work harder.

One way to do this is through something called "reciprocal inhibition." Basically, when one muscle contracts, the antagonist relaxes. So to somewhat switch off your hips flexors during abdominal training, all you have to do is contract your hamstrings and glutes.

With hamstring engagement during many ab exercises, the research shows 26 percent more activation of the lower rectus abdominis fibers and 46 percent more activation of external oblique fibers (1).

Here's a cool trick to help you do that during the classic ab roll-out:

Crushing a medball between your calves and hamstrings during roll-outs is an effective way to get your hammies firing. You'll instantly notice how this small upgrade can completely change the feel of your regular rollouts. As a bonus, it'll also add a small amount of resistance at the bottom of the movement.

How to Do It

  • Crush the medicine ball with your hamstrings. Squeeze your glutes. Imagine trying to crack a walnut with your butt cheeks throughout the rollout.
  • Brace hard in the bottom position.
  • Exhale fully at the top, pulling your ribs to your pelvis and flexing your spine at the top.

Related: The Ab-Building Trick Nobody Told You About

Related: 6 Core Exercises You Need


  1. Larson et. al. (2007). The Effect of Hamstring Contractions in the Activation of the Abdominal Muscles during a Standard Abdominal Crunch. Doctoral dissertation, University of North Dakota.